In monitoring properties of solutions, pH value, temperature, and electrical conductivity are important parameters. In general, measurement of pH value of water quality mostly uses an acid-base test paper, an acid-base indicator, or a glass electrode. The glass electrode mainly uses an ion-selective glass film as a sensor, and has a high selectivity for an ion or a type of ions. A front end of the electrode is a glass tube with a hollow hemispherical film wall. The film wall has a highly selectivity for hydrogen ions. An electrolyte is added to the glass tube and a reference electrode Ag/AgCl is contained in the electrolyte. By measuring a potential change, the pH value of the tested solution is obtained. In addition, in the temperature section, a glass thermometer or an infrared thermometer is mostly used. Further, the electrical conductivity can be measured using a glass electrode, and an electrical conductivity value is mainly measured by measuring resistance of the aqueous solution.
However, in the above common water quality measurement techniques, the glass electrode often has disadvantages that the sensing end is susceptible to acid and alkali, the response time is slow, the electrode maintenance is time-consuming, or the sensing end needs to immerse in a liquid when not used. Furthermore, corrections must be performed before using the glass electrode, including zero calibration of the neutral buffer solution (pH 7), sensitivity correction of pH value (pH 4 and pH 10), and temperature correction. Therefore, the glass electrode has many limitations in its use, and it is also not conducive to real-time measurement and monitoring of various water quality in response to the site environments.
Based on the above problem, the Applicant of the present application provided a solution property sensor (Taiwan Patent No. 1616655), which utilizes a single material to measure various characteristics of a solution. On a same material substrate, a plurality of sensing patterns are designed to simultaneously detect a pH value, temperature, and an electrical conductivity of a solution, to improve convenience and accuracy of measurement. However, when the above-mentioned technology is implemented in commercial applications, the solution property sensor has problems such as high manufacturing cost, complicated manufacturing process, poor package stability, and difficulty in maintaining waterproof characteristics for long-term use. In addition, the solution property sensor described above requires a laser engraving step to process a surface of an indium tin oxide (ITO) film, so as to produce a pH value sensing pattern, a temperature sensing pattern, and an electrical conductivity sensing pattern. Therefore, the process is complicated, and it is also necessary to consider the production yield and the connection characteristics of the measuring device. Furthermore, since material of the indium tin oxide film is not pure metal, the electrical connection capability is not as good as the metal connection point, so the electrical treatment at the connection end is a problem upon packaging.
As a result, it is necessary to provide a solution property sensor to solve the problems existing in the conventional technologies, as described above.